[PATCH v2 2/3] xen/x86: Split out page_walk_mfn() helper

[Jason Andryuk <jason.andryuk@xxxxxxx>]

do_page_walk() returns a mapping of the underlying address.  Split out
page_walk_mfn() which returns the mfn_ti, and have do_page_walk() use
that.

The new standalone page_walk_mfn() is generally useful for looking up the
MFN pointed to by an a virtual address.  It will be used in the x86 CPU
stub logic to determine if a stub page is already populated.

Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
---
 xen/arch/x86/include/asm/mm.h |  1 +
 xen/arch/x86/x86_64/mm.c      | 31 +++++++++++++++++++++----------
 2 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/include/asm/mm.h b/xen/arch/x86/include/asm/mm.h
index 06c20ab8de..6dc5115093 100644
--- a/xen/arch/x86/include/asm/mm.h
+++ b/xen/arch/x86/include/asm/mm.h
@@ -587,6 +587,7 @@ void audit_domains(void);
 void make_cr3(struct vcpu *v, mfn_t mfn);
 pagetable_t update_cr3(struct vcpu *v);
 int vcpu_destroy_pagetables(struct vcpu *v);
+mfn_t page_walk_mfn(unsigned long cr3, unsigned long addr);
 void *do_page_walk(struct vcpu *v, unsigned long addr);
 
 /* Allocator functions for Xen pagetables. */
diff --git a/xen/arch/x86/x86_64/mm.c b/xen/arch/x86/x86_64/mm.c
index 8eadab7933..d197dce9f8 100644
--- a/xen/arch/x86/x86_64/mm.c
+++ b/xen/arch/x86/x86_64/mm.c
@@ -59,29 +59,26 @@ extern unsigned int compat_machine_to_phys_mapping[];
 
 #endif /* CONFIG_PV32 */
 
-void *do_page_walk(struct vcpu *v, unsigned long addr)
+mfn_t page_walk_mfn(unsigned long cr3, unsigned long addr)
 {
-    unsigned long mfn = pagetable_get_pfn(v->arch.guest_table);
+    unsigned long mfn = cr3;
     l4_pgentry_t l4e, *l4t;
     l3_pgentry_t l3e, *l3t;
     l2_pgentry_t l2e, *l2t;
     l1_pgentry_t l1e, *l1t;
 
-    if ( !is_pv_vcpu(v) || !is_canonical_address(addr) )
-        return NULL;
-
     l4t = map_domain_page(_mfn(mfn));
     l4e = l4t[l4_table_offset(addr)];
     unmap_domain_page(l4t);
     if ( !(l4e_get_flags(l4e) & _PAGE_PRESENT) )
-        return NULL;
+        return INVALID_MFN;
 
     l3t = map_l3t_from_l4e(l4e);
     l3e = l3t[l3_table_offset(addr)];
     unmap_domain_page(l3t);
     mfn = l3e_get_pfn(l3e);
     if ( !(l3e_get_flags(l3e) & _PAGE_PRESENT) || !mfn_valid(_mfn(mfn)) )
-        return NULL;
+        return INVALID_MFN;
     if ( (l3e_get_flags(l3e) & _PAGE_PSE) )
     {
         mfn += PFN_DOWN(addr & ((1UL << L3_PAGETABLE_SHIFT) - 1));
@@ -93,7 +90,7 @@ void *do_page_walk(struct vcpu *v, unsigned long addr)
     unmap_domain_page(l2t);
     mfn = l2e_get_pfn(l2e);
     if ( !(l2e_get_flags(l2e) & _PAGE_PRESENT) || !mfn_valid(_mfn(mfn)) )
-        return NULL;
+        return INVALID_MFN;
     if ( (l2e_get_flags(l2e) & _PAGE_PSE) )
     {
         mfn += PFN_DOWN(addr & ((1UL << L2_PAGETABLE_SHIFT) - 1));
@@ -105,10 +102,24 @@ void *do_page_walk(struct vcpu *v, unsigned long addr)
     unmap_domain_page(l1t);
     mfn = l1e_get_pfn(l1e);
     if ( !(l1e_get_flags(l1e) & _PAGE_PRESENT) || !mfn_valid(_mfn(mfn)) )
-        return NULL;
+        return INVALID_MFN;
 
  ret:
-    return map_domain_page(_mfn(mfn)) + (addr & ~PAGE_MASK);
+    return _mfn(mfn);
+}
+
+void *do_page_walk(struct vcpu *v, unsigned long addr)
+{
+    mfn_t mfn;
+
+    if ( !is_pv_vcpu(v) || !is_canonical_address(addr) )
+        return NULL;
+
+    mfn = page_walk_mfn(pagetable_get_pfn(v->arch.guest_table), addr);
+    if ( !mfn_valid(mfn) )
+        return NULL;
+
+    return map_domain_page(mfn) + (addr & ~PAGE_MASK);
 }
 
 /*
-- 
2.54.0